Each round begins with a fresh Galaxian formation falling in to
place from the top of the screen. In order to finish each round,
your goal is to completely eliminate every Galaxian in sight.

Your ship will remain a set distance from the formation. You
can move left and right, but never up or down. You can fire exactly
one bullet at a time. As soon as the bullet hits an enemy or rises
off of the top of the screen, another bullet becomes available for
you to fire.

After a short while, Galaxians will peel off from the formation
and begin bombing raids on your ship. It is necessary to eliminate
them with fire, or avoid them when they reach your level of the
playfield. Once they fly off the screen (the bottom or either of
the sides,) they will reappear at the top a few seconds later and
typically return to their place in the formation.

As the Galaxians descend, they fire a few bullets of their own
at you. The bullets are only nominally faster than they are, but
collision with either one is equally deadly. If you do not feel
that you can safely eliminate the Galaxian in flight, it is best to
head towards the corner that is farthest from the direction that
the Galaxian is heading in. Be sure to account for who may be
coming behind the Galaxian closest to you.

As you eliminate more and more Galaxians, the intensity of the
bombing raids will increase, with more numbers of Galaxians
breaking from the formation to attack you. As you progress through
each round, the intensity and the frequency of the attacks also
increases.

Towards the end of a round, every Galaxian will break formation
and fly at you continuously. They will not even stop to return to
their formation. If a Flagship is one of the Galaxians left
remaining by the end of the round, it will attempt to escape. If it
succeeds, it will return with the next formation, resulting in a
third Flagship at the top instead of the usual two.